US4520315A - Nuclear spin tomography method - Google Patents

Nuclear spin tomography method Download PDF

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Publication number
US4520315A
US4520315A US06/413,962 US41396282A US4520315A US 4520315 A US4520315 A US 4520315A US 41396282 A US41396282 A US 41396282A US 4520315 A US4520315 A US 4520315A
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Prior art keywords
gradient
high frequency
pulse
frequency pulse
field gradient
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US06/413,962
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English (en)
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Wilfried Loeffler
Arnulf Oppelt
Horst Siebold
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Siemens AG
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Siemens AG
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Assigned to SIEMENS AKTIENGESELLSCHAFT, BERLIN AND MUNICH A GERMAN CORP. reassignment SIEMENS AKTIENGESELLSCHAFT, BERLIN AND MUNICH A GERMAN CORP. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: LOEFFLER, WILFRIED, OPPELT, ARNULF, SIEBOLD, HORST
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/4818—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space
    • G01R33/482—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space using a Cartesian trajectory
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56563—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0

Definitions

  • the invention relates to a nuclear spin tomography method according to the preamble of patent claim 1. Such a method is described e.g. in U.S. Pat. No. 4,070,611.
  • the body to be examined is exposed to a DC magnetic field B o and the nuclear isotopes to be be detected are excited to precession by means of a high frequency field B 1 .
  • the allocation of the nuclear resonance signal--detectable in a receiver coil as a consequence of the precession movement--to the location of its origin proceeds through the application of linear magnetic field gradients, such as are described e.g. by P. C. Lauterbur in "Nature” 242 (1973), pages 190/191. If G x is the intensity of the field gradient in the x-direction, the local nuclear resonance frequency ⁇ (x) results at:
  • the invention has the objective, in the case of a method according to the preamble of claim 1, with a given technically unavoidable inhomogeneity of the DC magnetic field, of producing a sectional image of a body which is optimum with regard to signal-to-noise ratio and freedom from artifacts.
  • FIG. 1 the block circuit diagram of an apparatus is schematically illustrated which is suitable for carrying out the inventive nuclear spin tomography method
  • FIG. 2 there is illustrated, in a diagram plotting the z-gradient signals G z (t) as a function of time, the sequence of the Hf- and z-gradient pulses, of a favorable pulse train;
  • FIG. 3 there is illustrated the corresponding sequence of the x-gradient pulses, G x (t);
  • FIG. 4 there is illustrated the corresponding sequence of y-gradient pulses for positive gradient effects k y ;
  • FIG. 5 there is illustrated the corresponding sequence of the y-gradient pulses for negative gradient effects k y ;
  • FIGS. 6 and 7 in a diagram, alternative switching sequences for the y-gradient are illustrated, whereby the latter is switched-on as long as possible;
  • FIGS. 8 and 9 there are illustrated, in diagrams, the pulse trains for projection-reconstruction-methods
  • FIG. 10 a variant for the y-gradient coil is illustrated
  • FIGS. 11 and 12 an alternative pulse train is illustrated in a diagram for which the current supply of the y-gradient must be designed in a bipolar fashion, and
  • FIGS. 13a-13d an example is illustrated of the excitation diagram for the purpose of simultaneous measurement of several layers.
  • FIG. 1, 1 and 2 characterize coils with which a DC magnetic field B o is generated in which, in the case of application for medical diagnostics, the body 5, to be examined of a patient is disposed.
  • gradient coils are associated with said patient which are provided for the purpose of generating independent, mutually perpendicular magnetic field gradients of the directions x, y, and z, according to the directions indicated at 6 in FIG. 1.
  • coils 7 and 8 are illustrated which, together with a pair of opposite similar coils, serve the purpose of generating an x-gradient.
  • the similar, not-illustrated y-gradient coils are disposed parallel to the body 5 and above as well as below said body and those for the z-gradient field are disposed transversely to the longitudinal axis at the head end and at the foot end.
  • the arrangement moreover, additionally contains a high frequency coil 9 serving the purpose of excitation of the nuclear resonance and reception of the nuclear resonance signals.
  • the coils 1 through 4, 7, 8 and 9, bordered by a dash-dot line 10, represent the actual examination instrument. It is operated from an electric arrangement which comprises a power supply unit 11 for the operation of the magnetic coils 1 through 4, as well as a gradient current supply 12 to which the coils 7 and 8, as well as the additional gradient coils, are connected.
  • the coil 9, serving the purpose of excitation as well as reception of the signal is connected, via a modulator 13 and a transmitter amplifier 14, to a radio-frequency oscillator 15, on the one hand, and, via a signal amplifier 16 and a phase-sensitive rectifier 17, to a process computer 18, on the other hand, from which, for the purpose of output of the image information, a viewing screen apparatus 19 is supplied.
  • additionally connections 20, 21, and 22, are provided between the computer 18 and the modulator 13, between the oscillator 15 and the rectifier 17, as well as between the computer 18 and the gradient current supply 12.
  • the duration of the pulse amounts to N times a basic time raster ⁇ t which is adjusted depending upon the intensity of the gradients and the thickness of the desired layer and which lies on the order of magnitude of 100 ⁇ s.
  • N is, for example, 128.
  • Gradient current pulses G x follow with a length of (N G - +N/2) ⁇ t, designated by 35 and 36, whereby the number N G - , must be so selected that, after the time N G - ⁇ t, the gradient current has reached its constant value after the rising edge. Simultaneously the y-gradient for a time N G - ⁇ t, referenced here with 40, is switched on.
  • the z-gradient for N/2 ⁇ t may be switched on.
  • the distribution of a nuclear resonance parameter can be calculated as a function of the location (x,y) by means of two-dimensional Fourier transformation from measured signal values S(t,N y ), if said signal values represent the Fourier coefficients S(k x ,k y ) of this distribution.
  • the variables k x and k y describe the wave numbers of the respective direction and are given by ##EQU1##
  • the double Fourier transformation thus yields a complex image value with imaginary part equal to zero in the ideal instance; i.e., an absolute sum-resolved locally in a sharp and high-contrast manner-of the complex image value, in case the above-cited interferences cause a phase rotation or a phase shift as a function of frequency over the image plane.
  • the pulse train employed according to FIG. 2 permits the generation of the entire value range of the wave numbers k x , k y (thus also the negative ones) with only one polarity of the gradient fields.
  • the electronics for the rapid switching of the gradient fields is very costly and would have to be separately installed per se for each polarity in case the polarity would have to be changed within a pulse train for the purpose of mensuration of positive and negative k x - and k y -components.
  • the first y-gradient pulse 40, or 42' (FIG. 5) respectively, additionally generates a phase/frequency characteristic in the y-direction:
  • the additional intervals in the y-gradient pulse thus ensure the linearity of the progression (or course) of the wave number k y as a function of the variable clock pulse number N y .
  • the second x-gradient commences with a time interval N G + ⁇ t, referenced with 37 in FIG. 3, while the gradient field stabilizes itself and the preamplifier at the receiver coil recovers from the 180°-Hf-pulse and the switching edge of the x-gradient.
  • N G + N G - ; otherwise, N G + can be selected a few clock pulses ⁇ t longer than N G - in order to compensate for the contribution of the drop-off edge of the prior x-gradient-forward pulse; instead, the scanning of the measured values can also be displaced (or shifted) by a corresponding time delay.
  • the magnetization has the form: M xy ⁇ exp [i ⁇ G y N y ⁇ t ⁇ y].
  • the z-gradient 33 after the 180°-Hf-pulse 32 serves the purpose of minimizing the phase shift over the layer thickness ⁇ z in order to thus generate an echo which is as strong as possible. In the case of symmetric 90°-Hf-pulses, this is accomplished by a negative z-gradient, or, as in our case, by a positive z-gradient after a 180°-Hf-pulse, which is approximately half as long as the 90°-Hf-pulse 31 (equal z-gradient field intensity assumed).
  • the signal is thus measured with the lowest-possible phase errors, and therefore also with an intensity hardly impaired by the basic field inhomogeneity.
  • the signal is attenuated only by the unavoidable phase shift which originates from the intended (or desired) gradient fields G x and G y .
  • the x-gradient is again switched on corresponding to the first readout interval (37', 38', 39').
  • the wave numbers k x again run from ⁇ G x ⁇ (-N/2) ⁇ t to ⁇ G x ⁇ (N/2-1) ⁇ t, as in the case of the first echo, the wave vector k y is now inverted, which must be taken into consideration in the computational processing.
  • FIGS. 6, 7. A second variant is illustrated in FIGS. 6, 7. Whereas, in the first variant, the y-gradients, at least N G , but otherwise as briefly as possible, are connected, in the case of the second variant, they are connected as long as possible; this is advantageous if the building-up time of the y-gradient field is very long.
  • the switching-on interval before the 180°-pulse varies from N G - ⁇ t to (N G - +N/2-1) ⁇ t, given a constant switching-on time of (N G + +N/2) ⁇ t after the 180°-pulse.
  • the switching-on period after the 180°-pulse is altered from (N G + +N/2-1) ⁇ t to N G + ⁇ t, whereas previously the switching-on time amounts constantly to (N G - +N/2) ⁇ t.
  • FIG. 10 the third variant of a possible circuit diagram for the y-gradient coil is illustrated which can be employed instead of the variant 1 of FIGS. 4 and 5.
  • Positive as well as negative wave numbers k y are attained through sole variation of the second y-gradient, whereas the first y-gradient before the 180°-Hf-pulse exhibits constant length.
  • FIGS. 8, 9 A pulse train for the production of a tomographic (or layer) image according to the projection-reconstruction method is illustrated in FIGS. 8, 9. It results from the pulse train according to FIG. 2 for the 2D-Fourier method essentially through the omission of the y-gradient pulses. Instead of the x-gradient field, a gradient field of equal intensity, but variable direction ⁇ is generated, whereby the angle ⁇ covers the x-y-plane and, with each operating cycle, is increased by an amount ⁇ . In case the rotation of the ⁇ -gradient field occurs through mechanical rotation of the coil arrangement, a monopolar current supply suffices.
  • the one amplitude G x must vary from cycle to cycle with cos ⁇ , the other G y with sin ⁇ . If ⁇ covers the angular range of 0 through 180°, then the current supply of the x-gradient coil must be designed in bipolar fashion.
  • the spectrum of the signal of an operating sequence (or cycle) is real under ideal conditions; in the case of interferences due to electronic phase errors and basic field-inhomogeneities, the sum of the complex spectrum can again be employed as real projection without deterioration of the imaging properties.
  • the additional intervals N G ensure the constancy of the gradient field intensity during the measured value detection.
  • the signal intensity is, on account of the central 180°-Hf-pulse, hardly attentuated by basic field inhomogeneities; several echoes can be measured in one operating sequence (or cycle). All described imaging methods can be modified to the extent that, through the selective 90° pulse, several parallel layers are simultaneously excited. The sign, or differently expressed the phase position, of the excitation is then successively varied for the individual, excited layers within an otherwise equal measuring sequence in order, with the aid of suitable decoding algorithms, to be able to obtain the signal conributions of the individual layers from the overall signal.
  • FIG. 13 illustrates as an example a suitable excitation sequence for the simultaneous mensuration of four layers. If S a -S d designate the aggregate signals obtained with these experiments, and S I to S IV designate the signals expected with excitation of each individual layer, then the following is valid:
  • (a) Scanning along successive lines of a selected layer is effected by the relative duration of an orthogonal field gradient (e.g. G y ) before and after the brief 180° high frequency pulse (e.g. 32, FIG. 2) in successive measurement cycles.
  • the intervals between the center of the 90° pulse at t-0 and the brief 180° pulse at t.sub. ⁇ 1 substantially corresponds to the interval between times t.sub. ⁇ 1 and t E1 .
  • each interval may be of of the order 1.5N ⁇ t (e.g. fifteen milliseconds).
  • the orthogonal field gradients may be switched on simultaneously following termination of the high frequency irradiation, and occupy a maximum time interval which may be less than the duration of the 90° pulse.
  • the G x pulse 35,36 may be on continuously for a time interval of slightly more than N/2 ⁇ t, e.g. slightly more than five milliseconds.
  • Multiple 180° pulses may follow each other, e.g. at intervals of the order of 3N ⁇ t or about thirty milliseconds.

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  • Physics & Mathematics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
US06/413,962 1981-09-07 1982-09-01 Nuclear spin tomography method Expired - Fee Related US4520315A (en)

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DE3135335A DE3135335A1 (de) 1981-09-07 1981-09-07 Kernspin-tomographie-verfahren
DE3135335 1981-09-07

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Cited By (16)

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US4613949A (en) * 1984-02-17 1986-09-23 General Electric Company Composite pulses for time reversal in NMR imaging
US4625170A (en) * 1983-08-01 1986-11-25 Hitachi, Ltd. NMR imaging method and apparatus
US4652824A (en) * 1983-03-21 1987-03-24 Siemens Aktiengesellschaft System for generating images and spacially resolved spectra of an examination subject with nuclear magnetic resonance
US4665365A (en) * 1985-01-07 1987-05-12 General Electric Company Method for reversing residual transverse magnetization due to phase-encoding magnetic field gradients
US4684892A (en) * 1985-04-22 1987-08-04 Siemens Aktiengesellschaft Nuclear magnetic resonance apparatus
US4689566A (en) * 1985-07-17 1987-08-25 Advanced Nmr Systems, Inc. NMR phase encoding using phase varying rf pulses
US4701710A (en) * 1984-06-07 1987-10-20 Siemens Aktiengesellschaft Nuclear magnetic resonance tomography apparatus
US4709211A (en) * 1985-07-11 1987-11-24 Kabushiki Kaisha Toshiba Nuclear magnetic resonance system
US4713615A (en) * 1985-08-30 1987-12-15 Resonex, Inc. Quantization error reduction method for phase encode gradient in NMR imaging
US4714887A (en) * 1985-04-26 1987-12-22 Siemens Aktiengesellschaft Nuclear magnetic resonance tomography apparatus
US4769603A (en) * 1985-08-19 1988-09-06 Siemens Aktiengesellschaft Method for the operation of a nuclear magnetic resonance apparatus
WO1998012964A1 (en) * 1996-09-25 1998-04-02 Cho Zang Hee Apparatus and method for silent magnetic resonance imaging with rotating gradient coil
US6081117A (en) * 1997-08-11 2000-06-27 Panacea Medical Laboratories Noise modulation for open access and remotely positioned MRI
US6157280A (en) * 1998-11-09 2000-12-05 Siemens Aktiengesellschaft Switchable gradient coil arrangement
USRE45725E1 (en) 2000-12-21 2015-10-06 University Of Virginia Patent Foundation Method and apparatus for spin-echo-train MR imaging using prescribed signal evolutions
USRE47178E1 (en) 2000-12-21 2018-12-25 University Of Virginia Patent Foundation Method and apparatus for spin-echo-train MR imaging using prescribed signal evolutions

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US4599565A (en) * 1981-12-15 1986-07-08 The Regents Of The University Of Calif. Method and apparatus for rapid NMR imaging using multi-dimensional reconstruction techniques
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JPS59200948A (ja) * 1983-04-30 1984-11-14 Toshiba Corp 核磁気共鳴映像装置
US4521733A (en) * 1983-05-23 1985-06-04 General Electric Company NMR Imaging of the transverse relaxation time using multiple spin echo sequences
US4549140A (en) * 1983-06-03 1985-10-22 General Electric Company Method utilizing combined, interleaved pulse sequences for reducing motion artifacts in computed T1,T2 and M0 NMR imaging
US4549139A (en) * 1983-06-03 1985-10-22 General Electric Company Method of accurate and rapid NMR imaging of computed T1 and spin density
US4621235A (en) * 1983-06-07 1986-11-04 U.S. Philips Corporation Method of and device for determining a nuclear magnetization distribution in a region of a body
EP0132337A3 (de) * 1983-07-21 1986-12-30 The Regents Of The University Of California Vorrichtung und Verfahren zur Verminderung des "Aliasing-Artefaktes" bei der sagittalen oder koronalen NMR-Bilderzeugung
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US4532474A (en) * 1983-09-09 1985-07-30 General Electric Company Nuclear magnetic resonance imaging using pulse sequences combining selective excitation and driven free precession
US4587489A (en) * 1983-10-07 1986-05-06 General Electric Company Method for rapid acquisition of NMR data
US4689562A (en) * 1983-10-11 1987-08-25 Elscint Ltd. NMR Imaging method and system
DE3340523A1 (de) * 1983-11-09 1985-05-15 Siemens AG, 1000 Berlin und 8000 München Kernspin-tomographiegeraet
EP0151026A3 (de) * 1984-01-31 1987-04-08 Kabushiki Kaisha Toshiba Verfahren zur Gewinnung von Bildsignalen mittels magnetischer Kernresonanz
DE3414634A1 (de) * 1984-04-18 1985-10-24 Bruker Medizintechnik Gmbh, 7512 Rheinstetten Verfahren zum anregen einer probe fuer die nmr-tomographie
JPS60222043A (ja) * 1984-04-20 1985-11-06 横河電機株式会社 核磁気共鳴による診断装置
JPS60222044A (ja) * 1984-04-20 1985-11-06 横河電機株式会社 核磁気共鳴による診断方法および装置
DE3429386A1 (de) * 1984-08-09 1986-02-27 Siemens AG, 1000 Berlin und 8000 München Kernspintomographiegeraet
DE3434161A1 (de) * 1984-09-18 1986-03-27 Bruker Medizintechnik Gmbh, 7512 Rheinstetten Verfahren zum messen der magnetischen kernresonanz
US4701707A (en) * 1984-10-26 1987-10-20 Siemens Aktiengesellschaft Magnetic resonance diagnostic device
JPS628747A (ja) * 1985-07-04 1987-01-16 株式会社東芝 磁気共鳴映像装置
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DE3632738A1 (de) * 1986-09-26 1988-03-31 Philips Patentverwaltung Verfahren zum bestimmen der spektralen verteilung der kernmagnetisierung in einem begrenzten volumenbereich
JPH05300895A (ja) * 1991-07-31 1993-11-16 Hitachi Medical Corp Ｍｒｉ装置における核スピンの選択励起方法
DE4213050C2 (de) * 1992-04-21 1994-03-03 Siemens Ag Verfahren zur Kompensation von Magnetfeldinhomogenitäten erster Ordnung bei Kernspintomographiegeräten
US5345178A (en) * 1992-04-21 1994-09-06 Siemens Aktiengesellschaft Method for setting the current through shim coils and gradient coils in a nuclear magnetic resonance apparatus

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Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4652824A (en) * 1983-03-21 1987-03-24 Siemens Aktiengesellschaft System for generating images and spacially resolved spectra of an examination subject with nuclear magnetic resonance
US4625170A (en) * 1983-08-01 1986-11-25 Hitachi, Ltd. NMR imaging method and apparatus
US4613949A (en) * 1984-02-17 1986-09-23 General Electric Company Composite pulses for time reversal in NMR imaging
US4701710A (en) * 1984-06-07 1987-10-20 Siemens Aktiengesellschaft Nuclear magnetic resonance tomography apparatus
US4665365A (en) * 1985-01-07 1987-05-12 General Electric Company Method for reversing residual transverse magnetization due to phase-encoding magnetic field gradients
US4684892A (en) * 1985-04-22 1987-08-04 Siemens Aktiengesellschaft Nuclear magnetic resonance apparatus
US4714887A (en) * 1985-04-26 1987-12-22 Siemens Aktiengesellschaft Nuclear magnetic resonance tomography apparatus
US4709211A (en) * 1985-07-11 1987-11-24 Kabushiki Kaisha Toshiba Nuclear magnetic resonance system
US4689566A (en) * 1985-07-17 1987-08-25 Advanced Nmr Systems, Inc. NMR phase encoding using phase varying rf pulses
US4769603A (en) * 1985-08-19 1988-09-06 Siemens Aktiengesellschaft Method for the operation of a nuclear magnetic resonance apparatus
US4713615A (en) * 1985-08-30 1987-12-15 Resonex, Inc. Quantization error reduction method for phase encode gradient in NMR imaging
WO1998012964A1 (en) * 1996-09-25 1998-04-02 Cho Zang Hee Apparatus and method for silent magnetic resonance imaging with rotating gradient coil
US6081117A (en) * 1997-08-11 2000-06-27 Panacea Medical Laboratories Noise modulation for open access and remotely positioned MRI
US6157280A (en) * 1998-11-09 2000-12-05 Siemens Aktiengesellschaft Switchable gradient coil arrangement
USRE45725E1 (en) 2000-12-21 2015-10-06 University Of Virginia Patent Foundation Method and apparatus for spin-echo-train MR imaging using prescribed signal evolutions
USRE47178E1 (en) 2000-12-21 2018-12-25 University Of Virginia Patent Foundation Method and apparatus for spin-echo-train MR imaging using prescribed signal evolutions
USRE48347E1 (en) 2000-12-21 2020-12-08 University Of Virginia Patent Foundation Method and apparatus for spin-echo-train MR imaging using prescribed signal evolutions

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EP0184225A2 (de) 1986-06-11
DE3135335A1 (de) 1983-08-18
EP0184225A3 (de) 1986-06-25
EP0074022B1 (de) 1987-11-25
EP0074022A1 (de) 1983-03-16

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